Method of manufacturing epitaxial silicon wafer and apparatus therefor

ABSTRACT

A method of forming an epitaxial layer to increase flatness of an epitaxial silicon wafer is provided. In particular, a method of controlling the epitaxial layer thickness in a peripheral part of the wafer is provided. An apparatus for manufacturing an epitaxial wafer by growing an epitaxial layer with reaction of a semiconductor wafer and a source gas in a reaction furnace comprising: a pocket in which the semiconductor wafer is placed; a susceptor fixing the semiconductor; orientation-dependent control means dependent on a crystal orientation of the semiconductor wafer and/or orientation-independent control means independent from the crystal orientation of the semiconductor wafer, wherein the apparatus may improve flatness in a peripheral part of the epitaxial layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.11/731,815 filed Mar. 30, 2007 now U.S. Pat. No. 8,021,484, which ishereby incorporated herein in its entirety by reference and is basedupon and claims the benefits of priorities from Japanese PatentApplication Nos. 2006-95717 and 2006-95718 filed on Mar. 30, 2006, theentire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus formanufacturing an epitaxial wafer, and more specifically relates to themethod and apparatus for manufacturing an epitaxial wafer with highflatness.

BACKGROUND

In general, the epitaxial silicon wafer has excellent characteristicssuch that neither defects arising from oxygen nor Grown-in defects(including COP) introduced during single crystal ingot growth areincluded in a surface epitaxial layer thereof where the device is made.

In recent years, epitaxial silicon wafers are being used forhigh-performance devices such as MPUs and flash memories andhigh-performance power devices such as MOS FETs and IGBTs. On the otherhand, high flatness is considered particularly important for improvementof semiconductor substrate quality and for preparation of amicrofabrication pattern in accordance with higher integration.

As for the epitaxial growth in a wafer in which high flatness isrequired, improvement in layer thickness uniformity is pursued by singlewafer processing. Moreover, layer thickness uniformization is furtherattempted by controlling the flow of gas for epitaxial growth by apartition and the like (for example, Japanese Unexamined PatentApplication Publication No. 2005-353665).

However, it is likely that the edge part of a silicon single crystalwafer to serve as a substrate shows an abrupt change in the thickness ofthe formed epitaxial layer and hence it is difficult to secure theflatness in the edge part.

Moreover, since it is likely that the vicinity of the edge part (or theouter circumferential part) of a semiconductor wafer (for example, asilicon single crystal wafer) to serve as a substrate shows an abruptchange in the thickness of the formed epitaxial layer due to variousfactors, and it is difficult to achieve the layer thickness uniformityonly by the uniformization of the flow of gas for epitaxial growth.

Therefore, a number of methods of optimizing epitaxial growth conditionsto reduce the unevenness in the distribution of the layer thickness havebeen proposed, but it is hard to say that they are good enough. Since aflattening process after the epitaxial growth cannot be performed whenthe grown wafer is found to have unsatisfactory flatness is obtained.Therefore, such wafer is deemed to be defective so as to become a waste.

For example, a method of manufacturing an epitaxial silicon wafer isproposed in which a substrate satisfying a desired flatness is sent to apredictive process of simulating the substrate flatness after epitaxialgrowth, the substrate determined to satisfy the substrate flatness afterthe layer formation as the objective is sent to the subsequent epitaxialgrowth process, and the substrate determined not to satisfy thesubstrate flatness is sent to the flattening process again (for example,Japanese Unexamined Patent Application Publication No. 2005-353665,Japanese Unexamined Patent Application Publication No. 2001-302395).

However, Japanese Unexamined Patent Application Publication No.2001-302395 does not disclose concretely a method of simulating filmformation in the epitaxial growth. In general, simulation of the layerformation is not necessarily easy since various factors interact witheach other. Therefore, it is very difficult, by using the method ofJapanese Unexamined Patent Application Publication No. 2005-353665, toperform the simulation in order to predict the flatness of the epitaxialsilicon wafer on which the epitaxial layer is formed.

SUMMARY OF THE INVENTION

In consideration of the aforementioned, an apparatus and a method forforming an epitaxial layer to improve uniformization of the thickness ofan epitaxial silicon wafer and, in particular, an apparatus and a methodfor controlling the epitaxial layer thickness of a wafer edge part maybe provided.

According to the present invention, the epitaxial layer thickness of thewafer edge part may be controlled and uniformized. This invention wasmade only after it was found that it was not sufficient just touniformize the flow of gas for the conventional epitaxial growth. Thatis, the present invention has a background that there are demands foruniformizing epitaxial layer thickness even in the edge part which iscut off conventionally in order to make the useable area of theepitaxial wafer wider. Even if thickness is uniform in the inner part ofa wafer, a huge change such as sharp reduction and the like of theepitaxial layer thickness at the outer circumferential part and itsvicinity may be caused in accordance with a huge change of the shape(for example a large change of thickness such as chamfered edge). Theflat area of the wafer may be made wider by shifting a point of thechange in the epitaxial layer thickness (thickness including thesubstrate) toward more outer circumferential side as far as possible. Itwas also found that the epitaxial layer thickness in the wafer edge partincreases or decreases periodically with respect to the crystalorientation. If this increase and decrease of the thickness would bereduced, the flat area of the wafer could be made larger. Here, theperiodic increase and decrease are caused by different formation ratesof the epitaxial layer according to the crystal orientation. Therefore,it is not sufficient just to uniformize the gas flow as a whole, but itis preferable to perform more precise control based on the crystalorientation.

The epitaxial layer thickness in the useful wafer edge part as mentionedabove may be controlled by using, independently or combinedly asappropriate, an orientation-dependent control method ororientation-dependent control means which changes along thecircumferential direction of the outer circumference of the wafer, or anorientation-independent control method or orientation-independentcontrol means which is independent of the circumferential direction ofthe outer circumference of the wafer. Further, the epitaxial layerthickness of this wafer edge part may be controlled by changing aperipheral member such as a wafer substrate and a susceptor;environmental condition such as a flow rate and concentration andtemperature of a raw material gas such as trichlorosilane; or acombination thereof.

The above-mentioned orientation-dependent control method ororientation-dependent control means includes, for example, according tothe crystal orientation, periodically changing or what is periodicallychanged in, the configuration and/or structure, other properties, or thelike of the susceptor fixed uniquely to the crystal orientation byfixing the semiconductor wafer substrate to the susceptor. On the otherhand, the orientation-independent control method ororientation-independent control means includes, for example, controllingor what is controlled in, the structure and/or shape of the susceptorand the environmental conditions from the crystal orientation.

The further features, characteristics, and various advantages of thepresent invention will be apparent with reference to the attacheddrawings and the following preferable embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross section view illustrating in general anepitaxial wafer manufacturing device according to the presentapplication.

FIG. 2 is a longitudinal cross section view illustrating in general asusceptor.

FIG. 3A is a plan view of a semiconductor wafer.

FIG. 3B is a view showing a crystal orientation of the semiconductorwafer.

FIG. 4A is a graph in which thickness of an epitaxial wafer is developedand plotted against angle.

FIG. 4B is a graph in which thickness of another epitaxial wafer isdeveloped and plotted against angle.

FIG. 4C is a graph in which autocorrelation function of layer thicknessof an epitaxial wafer with small outside disturbance of angleperiodicity is plotted against angle.

FIG. 4D is a graph in which autocorrelation function of layer thicknessof an epitaxial wafer with large outside disturbance of angleperiodicity is plotted against angle.

FIG. 4E is a graph in which average distribution of layer thicknessobtained by a folding method of 45-degree.

FIG. 4F is a graph in which static dispersion of distribution of layerthickness of grown epitaxial wafers in different temperatures.

FIG. 4G shows a contour map of static dispersion of distribution oflayer thickness of grown epitaxial wafers in different temperaturesagainst epitaxial temperature and trichlorosilane concentration.

FIG. 5 is a partially enlarged cross section view of portion of asusceptor where depth of spot facing is deep.

FIG. 6 is a partially enlarged cross section view of portion of thesusceptor where depth of spot facing is shallow.

FIG. 7 is a partially enlarged cross section view of portion of thesusceptor where pocket width is large.

FIG. 8 is a partially enlarged cross section view of portion ofsusceptor where pocket width is small.

FIG. 9 is a partially enlarged cross section view of portion of thesusceptor where thickness thereof is small.

FIG. 10 is a partially enlarged cross section view of portion of thesusceptor where thickness thereof is large.

FIG. 11 is a partially enlarged cross section view of portion of thesusceptor where a diameter thereof is small.

FIG. 12 is a partially enlarged cross section view of portion of thesusceptor where a diameter thereof is large.

FIG. 13 is a partially enlarged cross section view of portion of thesusceptor where depth of spot facing is deep according to Embodiment 1.

FIG. 14 is a partially enlarged cross section view of portion of thesusceptor where depth of spot facing is shallow according to Embodiment1.

FIG. 15 is a plan view of the susceptor of Embodiment 1.

FIG. 16 is a view showing developed depth of spot facing in thesusceptor of Embodiment 1.

FIG. 17 is a view showing developed distribution of layer thickness ofEmbodiment 1.

FIG. 18 is a partially enlarged cross section view of portion of thesusceptor where pocket width is small according to Embodiment 2.

FIG. 19 is a partially enlarged cross section view of portion of thesusceptor where pocket width is large according to Embodiment 2.

FIG. 20A is a plan view of the susceptor holding the semiconductor waferof Embodiment 2.

FIG. 20B shows a graph in which static dispersion of layer thicknessdistribution of epitaxial wafers grown in different trichlorosilaneconcentrations and temperatures.

FIG. 21A is a view showing developed distribution of layer thickness ofEmbodiment 2.

FIG. 21B is a view showing comparison of static dispersions of layerthickness distributions of epitaxial wafers formed by improved processand normal process.

FIG. 21C shows a graph in which layer thicknesses of epitaxial wafersformed in a high temperature and 2.3% of trichlorosilane concentrationwith normal and special susceptors are developed and plotted againstangle.

FIG. 21D shows a graph in which autocorrelation function of layerthickness distribution with the normal susceptor shown in FIG. 21C isplotted against angle.

FIG. 21E shows a graph in which autocorrelation function of layerthickness distribution with the special susceptor shown in FIG. 21C isplotted against angle.

FIG. 21F is a graph in which average distribution of layer thicknessobtained by the folding method of 45-degree.

FIG. 21G is a graph in which average distribution of layer thickness ofanother epitaxial wafer obtained by the folding method of 45-degree.

FIG. 22 is a partially enlarged cross section view of portion of thesusceptor where thickness thereof is small according to Embodiment 3.

FIG. 23 is a partially enlarged cross section view of portion of thesusceptor where thickness thereof is large according to Embodiment 3.

FIG. 24 is a bottom plan view of a susceptor of Embodiment 3.

FIG. 25 is a view illustrating developed thickness of the susceptor ofEmbodiment 3.

FIG. 26 shows a graph in which layer thickness of Embodiment 3 isdeveloped and plotted.

FIG. 27 shows a graph in which formed layer thicknesses on (110)epitaxial silicon wafers with the normal and special susceptors aredeveloped and plotted against angle.

FIG. 28A shows a graph in which autocorrelation function of thethickness distribution with the normal susceptor shown in FIG. 27 isdeveloped and plotted against angle.

FIG. 28B shows a graph in which autocorrelation function of thethickness distribution with the special susceptor shown in FIG. 27 isdeveloped and plotted against angle.

FIG. 29 illustrates a shape of the special susceptor.

FIG. 30 is a graph in which average distribution of layer thicknessshown in FIG. 27 obtained by the folding method of 45-degree.

FIG. 31 illustrates a longitudinal cross section view illustrating ingeneral a susceptor of Embodiment 4 and thickness distribution ofepitaxial layer formed with the susceptor.

FIG. 32 illustrates a longitudinal cross section view illustrating ingeneral a susceptor of Embodiment 5 and thickness distribution ofepitaxial layer formed with the susceptor.

FIG. 33 illustrates height distribution of a surface of a semiconductorwafer serving as a substrate, thickness distribution of the epitaxiallayer, and thickness distribution of the obtained epitaxial wafer.

DETAILED DESCRIPTION

In the following, the embodiments according to the present invention aredescribed in more detail with reference to the drawings. Like referencenumerals refer to like elements, and overlapping description is omitted.

FIG. 1 is a drawing schematically showing a longitudinal cross sectionof a susceptor 4. The bottom of a pocket 13 which is an opening of thesusceptor 4 comprises a shelf part and a tapered face as explained inthe following. For example, in an apparatus used for growing anepitaxial layer on a wafer having a diameter of 300 mm, a disk memberwith a diameter of 350 to 400 mm and a thickness of 3 to 6 mm is used asthe susceptor 4.

The pocket 13 of a circular recess is formed 20 to 40 mm inner towardthe center from the outer circumference of the top face of the susceptor4 such that the pocket receives a semiconductor wafer 12 which serves asa substrate and a tapered face 31 is provided on the bottom thereof. Thetapered face 31 is gently inclined.

A shelf part 32 which is formed in another circular recess is furtherprovided inside of the tapered face 31 toward the center. This shelfpart 32 is a circular flat face provided at slightly lower than thetapered face 31, and is a horizontal face parallel to the top face ofthe susceptor 4.

Three through-holes 22 are provided in the shelf part 32 although onlytwo of them are shown in FIG. 1 for convenience of explanation. Theupper part of each through-hole 22 forms a countersink hole 22′ which isexpanding and opening upward. Lift pins 23 for wafer support areinserted into the three through-holes 22, respectively. The borediameter of the through-holes 22 is made larger than the diameter of thelift pins 23 so that the lift pins 23 do not come in contact with thethrough-hole walls when the lift pins move up and down relative to thesusceptor 4.

The lift pins 23 is composed of quartz, carbon C, silicon carbide SiC,or the like. Each of the lift pins 23 has a shape of a pillar or acylinder, and is provided with a head 24 having a tapered face 24 b at alower outer circumference so as to fit the countersink hole 22′. Thetaper angle of the tapered face 24 b of this head 24 matches the taperangle of the tapered face of the countersink hole 22′.

The top part 24 a of the head 24 has a conical shape having an obtusevertex angle, and prevents generation of scratches on the rear surfaceof the wafer by the lift pins 23 by making very small a contact surfaceat the time of supporting the wafer rear surface. Each of the lift pins23 engages with the inner wall of the countersink hole 22′ of thesusceptor 4 at its head 24, and is suspended perpendicularly by selfweight in the state the lift pin 23 has descended. In this state, theupper part 24 a of the head 24 does not protrude from the upper surfaceof the shelf part 32.

FIG. 2 is a longitudinal cross section schematically showing thestructure of an epitaxial wafer manufacturing apparatus 1 where thesusceptor 4 and the like of FIG. 1 is used. In this epitaxial wafermanufacturing apparatus of single wafer type, the susceptor 4 (wafersupport table) which supports only one wafer horizontally is generallyprovided in a processing chamber 2. In order to transport a wafer 12onto the susceptor 4, a lift mechanism for moving the wafer 12 up anddown relative to the susceptor 4 is provided. The lift mechanism has aplurality of lift pins 23 which extend by penetrating the susceptor 4.The wafer 12 is placed on the upper end of these lift pins 23, and israised or lowered by moving the lift pins 23 up and down relative to thesusceptor 4. By using such a lift mechanism, the wafer 12 which has beenplaced on the hand of a transport arm and transported into the chamber 2can be transferred onto the susceptor 4 or, on the contrary, the wafer12 can be transferred from the susceptor 4 to the hand.

In order to grow an epitaxial layer, it is necessary to heat the wafer12 supported on the susceptor 4 to high temperature. For this purpose, anumber of heat sources 8 and 9 such as halogen lamps (infrared lamps)and the like are arranged to the upper and lower sides of the processingchamber 2 to heat the susceptor 4 and wafer 12.

The susceptor 4 is produced by applying a coating layer of siliconcarbide SiC to a substrate of carbon C, and serves as a uniformizingdisc for keeping the entire wafer 12 in the uniform temperature when thewafer 12 is being heated. As shown in FIG. 1, a pocket 13 which issomewhat larger than the wafer 12 and is a recess about 1 to 2 mm deepis formed on the upper surface of the susceptor 4 in order to store asilicon wafer, for example. The bottom face of this pocket 13 has atapered face so that the pocket 13 comes in contact only with the outercircumferential part of the semiconductor wafer 12, thereby reducing theface contact of the bottom face and wafer 12 to the utmost. An epitaxiallayer essentially consisting of a silicon thin film grows on the surfaceof the wafer 12 by accommodating the wafer 12 in this recess and holdingthe susceptor 4 at predetermined temperature in a carrier gas includingraw material gases. The raw material gases refer to a silicon source gasand dopant gas.

It is common to use a chlorosilane-based gas such as trichlorosilaneSiHCl₃ or dichlorosilane SiH₂Cl₂ for the silicon source gas, anddiborane (P-type) or phosphine (N-type) for the dopant gas. These gasesare introduced into the chamber with hydrogen H₂, which serves as acarrier gas.

The chamber 2 is formed by pressing a cylindrical base ring 3 from theupper and lower sides with a disc-like top window 5 and a lowersaucer-like window 6, and an internal closed space forms a reactor.Translucent quartz is used for the top window 5 and lower window 6 sothat light from heat sources may not be interrupted. The reactor formedin the chamber 2 is roughly divided into a top chamber 7 a which is aspace above the wafer 12, and a lower chamber 7 b which is a space belowthe wafer 12.

Further, heat sources 8 and 9 which heat the reactor are provided to theupper and lower sides of the chamber 2. In the present embodiment, theupper and lower heat sources 8 and 9 are respectively composed of aplurality of halogen lamps (infrared lamps).

The chamber 2 includes the susceptor 4 which supports the wafer 12 inthe upper part. When seen from the upper side, the susceptor 4 lookslike a disk, and the diameter thereof is larger than the wafer 12. Thepocket 13 which is a circular concave opening for storing the wafer 12is formed on the upper face of the susceptor 4. The susceptor 4 isproduced by applying a coating layer of silicon carbide SiC to asubstrate of carbon C, and serves as a uniformizing disc for keeping theentire wafer 12 in the uniform temperature when the wafer 12 is heated.Therefore, the susceptor 4 has a thickness and thermal capacity severaltimes those of the wafer 12. Moreover, the susceptor 4 stays generallyat temperature higher than the temperature of the wafer 12.

The susceptor 4 rotates around a vertical axis as a center of rotationin a surface parallel to the plate surface of the wafer 12 during anepitaxial layer growth treating operation so that a uniform epitaxiallayer may be formed on the upper face of the wafer 12. The center of thepocket 13 provided to the susceptor 4 coincides naturally with thecenter of rotation of the susceptor 4.

Below the susceptor 4, a cylindrical pillar-like or cylindricalsusceptor support shaft 14 to serve as the rotating axis of thesusceptor 4 is arranged perpendicularly, and at the upper part of thesusceptor support shaft 14, three susceptor arms 15 which support thesusceptor 4 horizontally are provided. The three susceptor arms 15 areradially arranged so that the arms form an angle of 120° when the arms15 are seen from the upper part, and upward projecting portions providedat the tip of respective susceptor arms 15 support the susceptor 4 byabutting with the lower surface of the susceptor 4.

The susceptor support shaft 14 is vertically arranged at a locationwhere the shaft axial center and the disk center of the susceptor 4coincide, and the susceptor 4 rotates by rotation of the susceptorsupport shaft 14. The rotation of the susceptor support shaft 14 isactivated by a rotation drive mechanism which is not shown. Thesusceptor support shaft 14 and susceptor arm 15 are formed oftranslucent quartz so that light from the lower heat source 9 may not beinterrupted.

(Measurement of Layer Thickness Distribution)

FIGS. 3A and 3B are the top views of a semiconductor wafer (siliconsingle crystal wafer) 12 to serve as the substrate of an epitaxialwafer. The semiconductor wafer 12 is set to a susceptor so that anepitaxial layer formation face (100) is directed upward. In order toexplicitly show the crystal orientation in the epitaxial layer formationface, a notch 12 a is stamped. When the crystal orientation isdesignated in the present description, layer thickness distribution ispresented in terms of crystal orientation and the like by assuming anoriginal point 12 b to be 0 degree and using angles up to 360 degreescounterclockwise, as shown in the top view of this semiconductor wafer12. FIG. 3B is a diagram showing the crystal orientation designated bythe Miller indices of the same wafer. This diagram shows thatmirror-symmetric crystal orientation is repeated every 45 degreesstarting from 0 degree, and crystal orientation is repeated with a 90degree cycle. Thus it is expected that crystal orientation-dependentlayer thickness distribution is repeated with a 90 degree cycle and achange having a mirror symmetry is repeated every 45 degrees.

FIG. 4A shows a graph in which a change of epitaxial layer formationthickness from an average layer thickness in terms of a ratio to a layerthickness target value is plotted as a function of the angle of FIG. 3(likewise in similar graphs to be described hereinafter). The verticalaxis represents the epitaxial layer formation thickness and thehorizontal axis represents the angle of FIG. 3. In the figure, blackcircles show epitaxial layer formation thickness at locations 1 mminward from the outer circumference, black triangles show epitaxiallayer formation thickness at locations 2 mm inward from the outercircumference, and crosses show epitaxial layer formation thickness atlocations 3 mm inward from the outer circumference, all as a function ofthe angles of FIG. 3A.

This epitaxial layer was formed by fixing the semiconductor wafer 12 asshown in FIG. 3A to a regular susceptor in an epitaxial wafermanufacturing apparatus of single wafer type shown in FIG. 2. Since ageneral type susceptor normally used for the apparatus of FIG. 2 wasalso used in this case, the structure and/or shape and the like in thevicinity of the inner circumferential face 13 b of the opening of apocket 13 does not change with a cycle of about 90 degrees, but stayedpractically uniform from 0 to 360 degrees.

The diagram shows that the thickness has maxima at 0 degree (360degrees), 90 degrees, 180 degrees, and 270 degrees, and valleys at 45degrees, 135 degrees, 230 degrees and 315 degrees. The influence ofcrystal orientation on a layer formation rate is evident. In particular,in the plot with black circles which represent data close to the outercircumference, this effect is large, and it turns out that the influencebecomes larger toward the outer circumference. Consequently, theuniformity of epitaxial layer thickness distribution of a wafer edgepart deteriorates due to layer thickness variation with angularperiodicity. Estimation of this degree of variation of the epitaxiallayer thickness distribution using the next formula (formula 1) showsthat the variation in the layer thickness distribution of the location 1mm apart from the outer circumference is Δt=2.01%.

$\begin{matrix}{{\Delta\; t} = \frac{\left( {{Max} - {Min}} \right)}{\left( {{Max} + {Min}} \right)}} & \left( {{Formula}\mspace{14mu} 1} \right)\end{matrix}$

FIG. 4B shows a plot of the thickness of the formed epitaxial layer at alocation 1 mm apart from the outer circumference toward the inside, inthe same way as in FIG. 4A. Black circles show a case where disturbancewithout angular periodicity is small, and crosses show a case wheredisturbance without angular periodicity is large. Similar to FIG. 4A,the vertical axis shows deviation of epitaxial layer thickness from thetarget value by taking a ratio to the layer thickness target value. Thatis, a thickness ratio of 0 means that the layer thickness is identicalto the target thickness, and a thickness ratio of +0.02 means that thelayer thickness is thicker than the target thickness by 0.02 as a ratioto the target thickness. Similarly to FIG. 4A, a graph plotted by blackcircles shows that thickness has maxima at 0 degree (360 degrees), 90degrees, 180 degrees and 270 degrees and valleys at 45 degrees, 135degrees, 230 degrees and 315 degrees. The influence of crystalorientation on the layer formation rate is evident. On the other hand, agraph plotted by crosses shows similar maxima, but a slow decline from 0to 360 degrees is also shown. In order to analyze periodicity in such aplot, the following regular autocorrelation function (formula 2) isused.

$\begin{matrix}{{R(\tau)} = {\int_{- \infty}^{\infty}{{{x(t)} \cdot {x\left( {t + \tau} \right)}}\ {\mathbb{d}t}}}} & \left( {{Formula}\mspace{14mu} 2} \right)\end{matrix}$

Formula (2) is used in the continuous system of signals. When a discretesystem in which signals are sampled is considered, the next Formula (3)is used.

$\begin{matrix}{{{R(k)} = {\frac{1}{N}{\sum\limits_{n = 0}^{N - 1}{{x(n)} \cdot {x\left( {n + k} \right)}}}}},\left\{ {{k = 0},1,2,\ldots\mspace{14mu},{N - 1}} \right\}} & \left( {{Formula}\mspace{14mu} 3} \right)\end{matrix}$

In this case, the layer thickness distribution in the circumferentialdirection can be expressed with a periodic function which returns to anoriginal value at 360 degrees, numerical processing using an originalmeasurement value at 360 degrees can be performed. Values of thusdetermined correlation function are plotted as a function of the anglein FIG. 4C (small disturbance without angular periodicity), and FIG. 4D(large disturbance without angular periodicity). In these graphs, thehorizontal axis stands for the angle, and the vertical axis shows therelative value obtained by taking a certain value as a reference. Thatis, a value of 0% is identical with the certain value taken as thereference, and a value of −0.002% is smaller than the value by 0.002%.These graphs show that maxima appear every 90 degrees and layerthickness distribution is changing with a 90 degree cycle. Comparison ofFIGS. 4C and 4D shows that the amplitude in FIG. 4C is considerablylarger.

Considering that the layer thickness distribution shows a change of 45degree symmetry as mentioned above, the data of FIG. 4B is re-arranged.That is, the data from 0 to 45 degrees is left as it is, and the datafrom 45 to 90 degrees is made to correspond to reversed data from 45degrees to 0 degrees, the data from 90 degrees to 135 degrees is made tocorrespond to the data from 0 to 45 degrees, the data from 135 degreesto 180 degrees is made to correspond to the reversed data from 45degrees to 0 degrees, the data from 180 degrees to 225 degrees is madeto correspond to the data from 0 to 45 degrees, the data from 225degrees to 270 degrees is made to correspond to the reversed data from45 degrees to 0 degrees, the data from 270 degrees to 315 degrees ismade to correspond to the data from 0 to 45 degrees, and the data from315 degrees to 360 degrees is made to correspond to the reversed datafrom 45 degrees to 0 degree. In the graph in which such data areplotted, homothetic curves may be drawn as they can be moved in parallelup and down to overlap with each other, and a group of curvesrepresenting data where disturbance without angular periodicity is largeshows larger variation in the upper and lower directions.

When the arithmetic mean (or arithmetic average) of the thicknesseswhich correspond to thicknesses of 0 to 45 degrees is calculated fordata which has small disturbance without angular periodicity, and datawhich is subject to large disturbance without angular periodicity andthe mean value is plotted in a range of 0 to 45 degrees, the data whichis subject to small disturbance without angular periodicity and the datawhich is subject to large disturbance without angular periodicity yieldhomothetic curves as they can be shifted upward and downward to overlapwith each other. When both sets of data are normalized using the layerthickness at 0 degree as a normalization factor and the layer thicknessratios are plotted in a range of 0 to 45 degrees, a graph shown in FIG.4E is obtained. This figure shows that the plotted data which is subjectto small disturbance without angular periodicity and the plotted datawhich is subject to large disturbance without angular periodicityroughly overlap with each other. Thus, it is made clear that disturbancewithout angular periodicity is practically independent of thedisturbance with angular periodicity. Moreover, it is expected that thevariation in layer thickness distribution can be reduced if thedisturbance with angular periodicity can be removed or canceled.

Next, the variation in the layer thickness distribution of epitaxialwafers which were prepared by changing trichlorosilane concentration andtemperature conditions was examined by using the same apparatus providedwith a susceptor having no angular periodicity. FIG. 4F shows thevariation of layer thickness distribution with angular periodicity ofthe edge part (1 mm from the edge part) when epitaxial growth isconducted by changing trichlorosilane concentration at high temperatureand low temperature. This diagram shows that, in the high temperaturegrowth, variation becomes smaller and a flat and preferable epitaxialwafer is prepared when trichlorosilane concentration is equal to orsmaller than 3.5%, more preferably equal to or smaller than 2%. Sincethe temperature in epitaxial growth contributes to layer thicknessdistribution with angular periodicity, it is not particularly necessaryto take baking temperature and the like into consideration. Here,epitaxial growth temperature is kept practically constant. Thetemperature of the wafer central portion read with a pyrometer, forexample, can be used for this epitaxial growth temperature. Although thetemperature which contributes to the layer thickness distribution withangular periodicity is considered to be the temperature of the edgepart, there is little temperature difference between the wafer centralportion and the edge part, and the temperature of the central portionmay be used in place of the temperature of the edge part. On the otherhand, the concentration of trichlorosilane (TCS) is the concentration ofthe trichlorosilane in a gas which is flowing in the upper part of aheat ring and the susceptor 4, and is calculated from the flow rates ofa source gas (when diluted in advance with a gas such as hydrogen, thedilution is to be taken into account) and a carrier gas (for example,the flow rate of each gas per 1 minute. Specifically, slm (standardliter/min), which is a unit showing the flow rate in terms of liter perminute at 1 atm and 0° C.). Since it is assumed here that the carriergas flowing in the lower part (10 b of FIG. 2) generally does not affecttrichlorosilane concentration, the carrier gas needs not to beconsidered when determining trichlorosilane concentration, but may beconsidered when the carrier gas substantially affects thetrichlorosilane concentration in a gas flowing in the upper part of thesusceptor 4. As described above, the present method makes the angularperiodicity of the layer thickness distribution of the resultingepitaxial wafer extremely small although the means without any angularperiodicity is used.

FIG. 4G relates to epitaxial wafers which were prepared by changing thetrichlorosilane concentration and temperature conditions and using thesame apparatus provided with the susceptor having no angularperiodicity. Here, a map describing the contour lines of variation inlayer thickness distribution with angular periodicity is shown as afunction of trichlorosilane concentration and temperature. In thisdiagram, the variation in layer thickness distribution with angularperiodicity becomes smaller in approaching the lower right part.Therefore, the trichlorosilane concentration and temperature conditionsin a triangle which is drawn on the lower right corner of the diagramand demarcated with a dashed line are preferred. The area within thistriangle can be expressed with the following formula, wherein C (%)represents trichlorosilane concentration and T represents temperature (°C.).C≧0.63T≦1160C≦0.0228×T−24.45  (Formula 4)

This graph is made with results of the product prepared by the sameapparatus provided with the susceptor having no angular periodicity.When a special susceptor is used as an orientation-dependent controlmeans, however, another diagram will be drawn as a function of aconcentration condition and a temperature condition. With such adiagram, the optimum manufacturing condition can be obtained on eachdevice condition by suitably combining the concentration condition andthe temperature condition.

Next, it is considered to set off differences in epitaxial growth due tothe crystal orientation by adopting a means with angular periodicity.For example, in order to reduce the variation in such layer thicknessdistribution, a susceptor having a structure and/or shape changing withthe variation of the layer thickness distribution can be used. In such asusceptor, specifically, the structure and/or shape in the vicinity ofthe inner circumferential face 13 b of a pocket opening part change by acycle of 90 degrees. More specifically, it is explained with referenceto FIGS. 5 to 12.

FIGS. 5 and 6 show the shape in the vicinity of the innercircumferential face 13 b of the opening of a susceptor in which onlythe spot facing depth of a pocket is changed within the same susceptor.FIG. 5 shows a partial enlarged cross section view at about 0 degree(360 degrees), 90 degrees, 180 degrees, and 270 degrees and FIG. 6 showsa partial enlarged cross section view at about 45 degrees, 135 degrees,225 degrees, and 315 degrees. In both cases, a semiconductor wafer 12 isheld so as to avoid face contact to the tapered face 31 of a susceptor4, and is arranged in a pocket 13 with a gap space 13 a.

When the spot facing depth D of the susceptor becomes shallower, asilicon source gas will be smoothly supplied to a wafer edge part, andthe epitaxial layer growth rate at the edge part becomes larger. Whenthe spot facing depth of the susceptor becomes larger, a reversephenomenon is seen and the growth rate becomes smaller. The position(height) of holding this semiconductor wafer 12 stays identical for thesusceptor 4. Hence, in order to change the spot facing depth of thepocket 13, the location of the upper surfaces 51 and 52 of a member inthe vicinity of the opening of the pocket is to be changed. That is, inFIG. 5, the upper surface of semiconductor wafer 12 is located at aposition lower than the upper surface 51 of the member in the vicinityof the opening of the susceptor 4, and the flow of a raw material gas(or source gas) shown by an arrow F1 is considered to bend roughly at aspot beyond the gap 13 a. Therefore, it is considered that flowstagnation X arises and the volume of gas supply in a circumference partdecreases by a small amount.

In FIG. 6, on the other hand, the upper surface of a semiconductor wafer12 is located at a position practically coplanar with the upper surface51 of a member in the vicinity of the opening of a susceptor 4. Thus, itis assumed that flow stagnation X does not takes place, a raw materialgas flows smoothly (F2) and an epitaxial layer formation rate isaccelerated sufficiently. In this instance, spot facing depth D may besubstantially equal to or smaller than the thickness of thesemiconductor wafer 12. Such a height ratio can be suitably determinedaccording to layer thickness distribution at the time of actuallyforming an epitaxial layer. In general, when the variation in the layerthickness distribution is larger, the height ratio is also made larger.The spot facing depth is preferably changed in a range of ±0.5 mm ofthickness in consideration of the thickness of the semiconductor wafer12. The state of FIG. 5 may change to the state of FIG. 6 in a curveand/or linearly. A shift from the state of FIG. 5 to the state of FIG. 6(or 6 to 5) is preferably made in a monotonically decreasing (ormonotonically increasing) way.

FIGS. 7 and 8 show the shape in the vicinity of the inner face 13 b ofthe opening of a susceptor, wherein only the width of a pocket 13 ischanged within the same susceptor. FIG. 7 shows a partial enlarged crosssection view at around 0 degree (360 degrees), 90 degrees, 180 degrees,and 270 degrees, and FIG. 8 shows a partial enlarged cross section viewaround 45 degrees, 135 degrees, 225 degrees and 315 degrees. In bothcases, a semiconductor wafer 12 is held so as to avoid face contact tothe tapered face 31 of a susceptor 4 and is arranged in a pocket 13 witha gap space 13 a. When the pocket width of the susceptor becomes larger,a silicon source gas is smoothly supplied to a wafer edge part, and theepitaxial layer growth rate of the edge part becomes larger. When thepocket width of the susceptor becomes smaller, a reverse phenomenon isseen and the growth rate becomes smaller. Since this semiconductor wafer12 has a substantially round shape (disk shape), the interval L of thegap 13 a changes when the pocket width is changed. Therefore, it isplausible that the flow of a raw material gas (or source gas) shown byan arrow F3 reaches the upper surface of the semiconductor wafer 12after passing over the outer circumferential part of the semiconductorwafer 12 (FIG. 7). On the other hand, it is plausible that the flow ofthe raw material gas (or source gas) shown by an arrow F4 reaches theupper surface of semiconductor wafer 12 at a location beyond the gapapace 13 a which opens by an interval of L (FIG. 8). That is, the regionof stagnation X deviates from the semiconductor wafer 12.

Such a pocket width ratio can be suitably determined according to layerthickness distribution at the time of actually forming an epitaxiallayer. In general, when the variation in the layer thicknessdistribution is larger, the width ratio is also made larger. The pocketwidth is preferably changed in a range of +1 to 10 mm of the diameter ofthe semiconductor wafer 12. The state of FIG. 7 may change to the stateof FIG. 8 in a curved manner and/or a linear manner. A shift from thestate of FIG. 7 to the state of FIG. 8 (or 8 to 7) is preferably made ina monotonically decreasing (or increasing) way.

FIGS. 9 and 10 show the shape in the vicinity of an opening, whereinonly thickness within the same susceptor is changed to change thermalcapacity. FIG. 9 shows a partial enlarged cross section around 0 degree(360 degrees), 90 degrees, 180 degrees, or 270 degrees and FIG. 10 showsa partial enlarged cross section view around 45 degrees, 135 degrees,225 degrees, or 315 degrees. In both cases, a semiconductor wafer 12 isheld so as to avoid the face contact with the tapered face 31 of asusceptor 4 and is arranged in a pocket 13 with a gap space 13 a. Whenthe thickness of the susceptor becomes larger, or when the diameterthereof becomes larger, the thermal capacity of the susceptor in thisportion increases, and an epitaxial layer growth rate becomes larger.When the thickness of the susceptor becomes smaller, or when thediameter thereof becomes smaller, a reverse phenomenon is seen, and thegrowth rate becomes smaller. Since this semiconductor wafer 12 has asubstantially round shape (disk shape), the shape of the radialdirection in the vicinity of the opening of the susceptor 4 is alsouniform. However, when, as shown in FIG. 10, height H is made larger byabout 20% compared with that of FIG. 9, thermal capacity will alsobecome larger according to the thickening. Since the shape of the flowpath of a raw material gas (or source gas) does not change, raw materialsupply is independent of crystal orientation. However, it may beutilized that the rate of epitaxial layer formation becomes larger whenthe heat capacity is larger.

Such differences in the thermal capacity is smoothened to some extenteven if the susceptor 4 is a single block on the whole and the shapethereof is abruptly changed linearly. Thus such a structure is aneffective means when a gentle shift is required.

FIGS. 11 and 12 show the shape in the vicinity of the opening of asusceptor of another type in which thermal capacity is changed. FIG. 11shows a partial enlarged cross section view at about 0 degree (360degrees), 90 degrees, 180 degrees, or 270 degrees and FIG. 6 shows apartial enlarged cross section view at about 45 degrees, 135 degrees,225 degrees, or 315 degrees. In both cases, a semiconductor wafer 12 isheld so as to avoid the face contact with the tapered face 31 of asusceptor 4 and is arranged in the pocket 13 with a gap space 13 a.Since this semiconductor wafer 12 has a substantially round shape (diskshape), the shape of the radial direction in the vicinity of the openingof the susceptor 4 is also uniform. However, when width W issignificantly enlarged as shown in FIG. 12 compared with the width ofFIG. 11, the thermal capacity will also become large. Since thesusceptor of FIG. 12 has a little longer flow path of a raw material gas(or source gas), reduction of the supply rate caused by flow resistancemay also occur simultaneously, but the shape is suitably selected byusing experimental results. Since the mechanism is the same as theabove-mentioned mechanism, explanation thereof is omitted here.

As mentioned above, the layer thickness distribution of the epitaxiallayer of the edge part can be improved by applying, to the susceptor,the above processing which cancels the angular dependence of the growthrate of the epitaxial layer of the wafer edge part. Wafers of variouscrystal orientations and chamfer shape can be made usable by adjustmentof spot facing depth, pocket width, and thermal capacity (depth, width,thickness, an angle of applying processing).

Example 1

FIGS. 13 to 17 show layer thickness distribution when an epitaxial layeris formed by changing spot facing depth. Duplicated explanation thereofis omitted because of similarity to FIGS. 5 and 6. FIGS. 13 and 14 showa partial enlarged cross section of a susceptor and the like, and FIG.15 is a top view of the susceptor 4. FIG. 16 is a graph showing spotfacing depth and being developed with respect to the angle. The spotfacing depth of the present case is made smaller at shallow parts thanthe thickness D1 of a semiconductor wafer 12. As shown in FIGS. 15 and16, the spot facing depth changes with a cycle of about 90 degrees.

In a (100) substrate (notch direction 0°) which is the semiconductorwafer, the growth rate of the epitaxial layer of an edge part becomesgradually slower as the direction changes from 0° to 45°. The susceptorwas machined so as to minimize the spot facing depth of the portion inwhich the direction of 45° of the wafer is located when the wafer isloaded on the susceptor, and then epitaxial growth was undertaken. FIG.17 shows that layer thickness variation depending on the crystalorientation decreases considerably. When the layer thicknessdistribution of a location 1 mm inner from the outer circumference isestimated by using the above formula (formula 1), Δt was found to havebeen improved from 2.01% to 0.88%.

Example 2

FIGS. 18 to 20A and 21A show layer thickness distribution when anepitaxial layer is formed by changing pocket width. Duplicatedexplanation is omitted because of similarity to FIGS. 7 and 8. FIGS. 18and 19 show a partial enlarged cross section view of a susceptor and thelike, and FIG. 20 is a top view of the susceptor 4. FIG. 21A is a graphshowing the effect of pocket width on layer thickness and beingdeveloped with respect to the angle. The pocket width in this experimentis made slightly wider than the radius of a semiconductor wafer 12 at anarrow part, and about 5 mm wider than the above diameter at a widepart. As shown in FIG. 20A, the pocket width changes with a cycle of 90degrees.

In a (100) substrate (notch direction 0°) which is a semiconductorwafer, the growth rate of the epitaxial layer of an edge part becomesgradually smaller as the direction changes from 0° to 45°. The susceptorwas machined so as to maximize the pocket width of the portion in whichthe direction of 45° of the wafer is located when the wafer is loaded onthe susceptor, and then epitaxial growth was undertaken. FIG. 21A showsthat layer thickness variation depending on crystal orientationdecreases considerably. When the layer thickness distribution of alocation 1 mm inner from the outer circumference is estimated by usingthe above formula (formula 1), Δt was found to have been improved from2.01% to 0.97%.

Here, in FIGS. 20A, 20B, and 21B, the relationship between the magnitudeof the gap 13 a being the difference between the susceptor and thepocket width and the variation of layer thickness distribution withangular periodicity is explained. As shown in FIG. 20A, the pocket widthat a location separated counterclockwise by 45° rotation from thereference point is wider than the pocket width at a location separatedcounterclockwise by 90° rotation. FIG. 20B is obtained by taking thedifference of this width on the horizontal axis and the variation inlayer thickness distribution with angular periodicity on the verticalaxis. In preparation of this epitaxial wafer, data of a wafer grown atlow temperature is shown with white rhombi, and other data sets are forwafers grown at high temperature. White squares represent a wafer grownwith a trichlorosilane concentration of 1.60%, and white trianglesrepresent a wafer grown with a trichlorosilane concentration of 2.33%.The wafer grown at the low temperature (white rhombi) was subjected toepitaxial formation also at a trichlorosilane concentration of 2.33%.White circles are for 3.66% and black squares are for 7.14%.

In this graph, respective measurement points are plotted. From theplots, a several order approximate expression was derived by the leastsquare method, which approximate expression is then used for connectingplotted points. When the variation in thickness distribution withangular periodicity is observed as a function of a certain optimumsusceptor-pocket width difference, every plotted curve shows a minimumat a certain susceptor-pocket width difference, and variation becomeslarger when the difference is excessively large or small. For the sameconcentration, the high temperature growth shows a minimal value ofabout 0.1% when the pocket width difference is about 1.5 mm. On theother hand, the low temperature growth shows a minimal value of about0.3% when the pocket width difference is about 3 mm. The above resultsshow that it is easier at higher temperature to adjust the growth ratedifference due to crystal orientation without making the pocket widthdifference large. It is also found that the minimum magnitude ofvariation is smaller at higher temperature. If growth temperature isfixed at the high temperature, it turns out that the susceptor-pocketwidth difference becomes smaller when the TCS concentration is lower.However, practically the same susceptor-pocket width difference ispreferable when the TCS concentration is 3.66% or more. Once such adiagram is plotted, it is understood how much difference should beprovided between the susceptor and the pocket width.

FIG. 21B shows the effect of an improved process and a normal process onvariation. As shown in this graph, it is clear that the improved process(raw material concentration and temperature) is required in order tomake variation in the layer thickness distribution with angularperiodicity 0.5% or smaller.

FIG. 21C shows layer thickness distributions with the angularperiodicity as a function of the angle of FIG. 3A when the epitaxialformation is conducted with a normal susceptor and a special susceptorat high temperature and at trichloroethylene concentration of 2.3%. Thespecial susceptor was built by the method mentioned above so that thevariation in layer thickness distribution with the angular periodicityis reduced. As shown in this diagram, the layer thickness distributionwith angular periodicity changes with a cycle of about 90 degrees whenthe regular susceptor is used, but such a result is not necessarilyobtained for the special susceptor.

Each of FIGS. 21D and 21E shows a graph in which an autocorrelationfunction is plotted as a function of an angle, in a similar manner as inFIGS. 4C and 4D. The normal susceptor clearly shows a periodicity of 90degrees. In the special susceptor, periodicity cannot be recognizedclearly although inconspicuous maxima are seen at every 90 degrees.Further, the rate of change of the autocorrelation function of thespecial susceptor is considerably smaller than that of the normalsusceptor. FIG. 21F shows an average epitaxial layer thickness ratioobtained by the 45-degree fold back which was determined in a similarway as mentioned with respect to FIG. 4E. This graph shows that thevariation in layer thickness distribution with angular periodicity isreduced when the special susceptor is used. Further, angular periodicityis inconspicuous, and reduction of this variation means that thedifference in the epitaxial formation rate based on crystal orientationhas been canceled by using the special susceptor. FIG. 21G shows anaverage epitaxial layer thickness ratio obtained by the 45-degree foldback when the epitaxial formation is performed at the low temperature.It is seen that, compared with FIG. 21F, the variation of the layerthickness ratio is larger to a certain extent. However, it is alsonoticed that the variation in layer thickness distribution with angularperiodicity is reduced when the special susceptor is used, even inepitaxial formation at the low temperature. The figure further showsthat the difference of the epitaxial formation rate based on the crystalorientation has been canceled by using the special susceptor.

Example 3

FIGS. 22 to 26 show layer thickness distribution as an epitaxial layeris formed by changing thermal capacity (partial thickness of susceptor).Duplicated explanation thereof is omitted because of the similarity toFIGS. 9 and 10. FIGS. 22 and 23 show a partial enlarged cross sectionview of a susceptor and the like, and FIG. 24 is a schematic diagram ofthe bottom of the susceptor 4. FIG. 25 shows the variation of susceptorthickness developed with respect to the angle. FIG. 26 is a graphshowing the effect of susceptor thickness on layer thickness developedwith respect to the angle. In this susceptor, the partial thickness of athick portion is about 20% larger than the partial thickness of a thinportion. As FIGS. 24 and 25 show, the thickness of the susceptor changeswith a cycle of about 90 degrees.

In a (100) substrate (notch direction 0°) which is a semiconductorwafer, the growth rate of the epitaxial layer of an edge part becomesgradually smaller as the direction changes from 0° to 45°. The susceptorwas machined so as to maximize the thickness of the portion in which thedirection of 45° of a wafer is located when the wafer is loaded on thesusceptor, and then epitaxial growth was undertaken. FIG. 26 shows thatthe variation of layer thickness depending on the crystal orientation isdecreased considerably. When the layer thickness distribution of alocation 1 mm inner from the outer circumference is estimated by usingthe above formula (formula 1), Δt was found to have been improved from2.01% to 1.10%.

The flatness of an epitaxial wafer to be manufactured can be improved bycombining with the thin and thick portions of the epitaxial layerformation surface of the semiconductor wafer to serve as a substrate.

FIG. 27 shows the layer thickness distribution with the angularperiodicity as a function of the angle of FIG. 3A when the epitaxialformation is conducted with a silicon wafer substrate having a (110)upper surface and using a regular susceptor and a special susceptor. Thespecial susceptor was prepared by the method mentioned above so that thevariation in the layer thickness distribution with angular periodicityis reduced. As shown in this graph, the layer thickness distributionwith the angular periodicity changes with a cycle of about 180 degreeswhen the regular susceptor is used, but such a result is not necessarilyobtained for the special susceptor.

Each of FIGS. 28A and 28D shows a graph in which each autocorrelationfunction is plotted as a function of the angle. The plotted data isbased on layer thickness distributions obtained when the normalsusceptor and special susceptor of FIG. 27 are respectively used in asimilar way as described in FIGS. 4C and 4D. The normal susceptorclearly shows a periodicity of 180 degrees. In the special susceptor,the periodicity cannot be recognized clearly although inconspicuousmaxima are seen at every 90 degrees. Further, the rate of change of theautocorrelation function of the special susceptor is considerablysmaller than that of the normal susceptor.

Here, the relationship between the silicon wafer substrate and thespecial susceptor is explained using FIG. 29. FIG. 29 shows a siliconwafer substrate ((a)) placed on the special susceptor of the directionof 0 degree as shown in the top plan view ((c)). FIG. 29 shows a siliconwafer substrate ((b)) placed on the special susceptor of the directionof 90 degrees shown in the top plan view ((c)). As shown in FIG. 29, thegap space is larger in the direction of 90 degrees (or the direction of270 degrees). Consequently, the epitaxial formation rate in thedirection of 90 degrees (or the direction of 270 degrees) is increased.

FIG. 30 shows an average epitaxial layer thickness ratio obtained by the45-degree fold back method as described in a similar way as in FIG. 4E.This graph shows that the variation in the layer thickness distributionwith the angular periodicity is reduced when the special susceptor isused. Further, the angular periodicity is absent, and reduction of thisvariation means that the difference in the epitaxial formation ratebased on crystal orientation can be canceled by using the specialsusceptor.

As described above, even if the crystal face of epitaxial formation of asilicon wafer substrate is (110), the variation in the thicknessdistribution with the angular periodicity becomes small if the specialsusceptor is used, and the difference in the epitaxial formation ratebased on the crystal orientation can be canceled with the specialsusceptor. Thus, no matter what the crystal face of the epitaxialformation of the silicon wafer substrate may be, it is possible toflatten the layer thickness by the special susceptor.

Example 4

FIG. 31 shows a schematic diagram in which enlargement of the right endpart of the susceptor 4 of FIG. 1 is displayed, and further a graph ofepitaxial layer thickness distribution formed with the presentapparatus. This susceptor 4 has a pocket width of 302 mm. The ledgelength L of a ledge (‘Ledge’) part 33 provided with a tapered face 31 is6.0 mm. The width of a space 13 a defined by the outer circumferentialface of a semiconductor wafer 12, the tapered face 31 and the innercircumferential face of a pocket 13 is about 1 mm. The epitaxial layerthickness formed with such an apparatus reaches a minimum at a locationabout 145 mm from the center of the wafer 12, and then increases rapidlyfrom there. In this case, the thickness distribution of the epitaxiallayer of the outer circumferential part in a device use field was 0.90%.Here, the vertical axis of FIG. 3 shows a change from the mean value ofepitaxial layer thickness as a relative value with respect to thethickness of an objective epitaxial layer. The vertical axis of similargraphs in the following has the same meaning.

Example 5

Although FIG. 32 shows basically the same drawing as FIG. 31 does, theledge length L of a ledge (‘Ledge’) part 33 provided with a tapered face31 is made to be 3.0 mm. The width of a space 13 a defined by the outercircumferential face of a semiconductor wafer 12, the tapered face 31and the inner circumferential face of a pocket 13 is about 1 mm. When aseveral micrometer-thick epitaxial layer was formed with such anapparatus, the thickness of the formed epitaxial layer reached a minimumat a location about 148 mm from the center of the wafer 12, and thenincreased rapidly from the location.

If the area to be utilized in the prepared epitaxial wafer is an area 2mm or more inner from the outer circumference of this wafer (that is, anarea 2 mm from the edge is cut off), for example, the thickness of theepitaxial layer of Example 2 becomes minimum at the boundary. That is,if the length L of the ledge part 33 is made to be 3.0 mm, a point Qwhere the thickness shows a minimum will not be included in the area tobe utilized for the device. In this case, the thickness distribution ofthe epitaxial layer in the circumferential part in an area to beutilized for a device has improved from 0.90% of Example 4 to 0.53% ofExample 5.

Example 6

FIG. 33 shows a case where the ledge length L of a ledge (‘Ledge’) part33 is made to be 4.0 mm in a susceptor 4 having a pocket width of 302mm. When an epitaxial layer having a thickness of several microns isformed using this susceptor 4 while keeping other preparation conditionsidentical with those of the above example, a thickness distribution ofan epitaxial layer as shown in (b) of FIG. 33 was obtained. Layerthickness reached a minimum at a location 147 mm from the center (3 mmfrom the edge). In this example, a semiconductor wafer 12 to serve as asubstrate had a thickness as shown in (a) of FIG. 33 on the epitaxiallayer formation surface. The surface height of this wafer had thehighest point at a location about 147 mm from the center (3 mm innerfrom the edge). The thickness distribution of the epitaxial wafer formedof a combination of such a substrate and a layer is shown in (c) of FIG.33. The graph shows that the flatness of the epitaxial wafer resultingfrom such a combination is high.

As mentioned above, the thickness of the formed epitaxial layer can bechanged by changing the length of the ledge part. In particular, it ispossible to control the location from which the increase in thickness ofthe epitaxial layer in the vicinity of the outer circumference of anepitaxial wafer starts, and the extent of the increase. Since the ledgelength is freely changeable as far as the function of a ledge part ofholding the semiconductor wafer is satisfied, the control is made easy.Further, if a ledge length which fits the substrate shape is selected,it is possible to keep the flatness in the area to be utilized for adevice high up to the vicinity of the edge part.

The flatness of the epitaxial wafer to be manufactured can be improvedby a combination with thin and thick portions of the epitaxial formationsurface of the semiconductor wafer to serve as a substrate. It is alsopossible to set off the differences in an epitaxial formation rate dueto the difference in the crystal orientation by utilizing the differencein the epitaxial formation thickness due to the difference in the lengthof such a ledge part. Moreover, such techniques may be combined toprovide an epitaxial silicon wafer with high flatness.

In addition to the above, the following may be included in the presentinvention.

(1) An apparatus for manufacturing an epitaxial wafer by growing anepitaxial layer with reaction of a semiconductor wafer and a source gasin a reaction furnace comprising: a pocket having an opening in whichthe semiconductor wafer is placed; a susceptor for holding thesemiconductor wafer; and an orientation-dependent control meansdependent on a crystal orientation of the semiconductor wafer and/or anorientation-independent control means independent from the crystalorientation of the semiconductor wafer, wherein the apparatus mayincrease flatness in a peripheral part of the epitaxial layer.

(2) The apparatus for manufacturing the epitaxial wafer according to theabove (1), wherein the orientation-dependent control means comprises thesusceptor having a structure and/or shape changing periodically near aninner face of the opening to a change of a crystal orientation of thesemiconductor wafer.

(3) The apparatus for manufacturing the epitaxial wafer according to theabove (2), wherein the susceptor has a spot facing with a depth thereofchanging near the inner face of the opening in synchronization with thechange of the crystal orientation of the semiconductor wafer.

(4) The apparatus for manufacturing the epitaxial wafer according toabove (2), wherein the pocket has a width changing near the inner faceof the opening in synchronization with the change of the crystalorientation of the semiconductor wafer.

(5) The apparatus for manufacturing the epitaxial wafer according to theabove (2), wherein the susceptor has a width changing near the innerface of the opening in synchronization with the change of the crystalorientation of the semiconductor wafer.

(6) The apparatus for manufacturing the epitaxial wafer according to anyone of the above (1) to (5), wherein the orientation-independent controlmeans comprises a ledge part extending inwardly inside of the opening ofthe susceptor for a predetermined length, the ledge part provided in alower part of the opening such that the semiconductor wafer is placed,the ledge part having the predetermined length; and/or a shape in aperipheral part of the semiconductor wafer.

(7) The apparatus for manufacturing the epitaxial wafer according to theabove (6), wherein the predetermined length of the ledge part is equalto or more than 2 mm and less than 6 mm.

(8) The apparatus for manufacturing the epitaxial wafer according to anyone of the above (1) to (7), wherein the orientation-independent controlmeans comprises a control device capable of controlling a raw materialconcentration and/or a temperature wherein the raw materialconcentration is equal to or less than a predetermined concentrationand/or the temperature is equal to or more than a predeterminedtemperature.

Here, the predetermined concentration is, for example, equal to or lessthan 3.5% if trichlorosilane is utilized and the orientation-dependentcontrol means is not used. And it is more preferable to be 2.5% or less.Further, it is preferably 1.5% or less. Here, in general, as the sourcegas concentration is lowered, the epitaxial formation rate is alsolowered such that it is more preferable to make the concentration higherto increase the productivity in an industrial view point. Also, thepredetermined temperature is, for example, preferably 1100 Celsius orhigher. More preferably, it is 1110 Celsius or higher. Even morepreferably, it is 1120 Celsius or higher. In particular, when theconcentration is less than 1.5%, it is preferable to be 1120 Celsius orhigher. Here, in general, at higher temperature, the grown epitaxiallayer tends to have a rough surface, which is not preferable. Thus, ifthe orientation-dependent control means is not used, it is possible todetermine the preferable condition as a whole in consideration ofreduction of variation in the layer thickness distribution of the angleperiodicity, industrial productivity, quality of the product, and thelike. Also, when the orientation-dependent control means is used, suchconcentration condition and temperature condition are suitably combinedto determine the optimum manufacturing condition.

(9) A method of manufacturing an epitaxial wafer by growing an epitaxiallayer with reaction of a semiconductor wafer and a source gas in areaction furnace comprising the steps of: providing the semiconductorwafer from an opening of a pocket of a susceptor; fixing thesemiconductor wafer to the susceptor of an epitaxial wafer manufacturingapparatus, the susceptor comprising: an orientation-dependent controlmeans dependent on a crystal orientation of the semiconductor waferand/or an orientation-independent control means independent from thecrystal orientation of the semiconductor wafer; and forming an epitaxiallayer as the susceptor is rotated with the semiconductor wafer.

(10) The method of manufacturing the epitaxial wafer according to theabove (7), the orientation-dependent control means comprises thesusceptor having a structure and/or shape changing periodicallyaccording to the change of the crystal orientation of the semiconductorwafer.

(11) The method of manufacturing the epitaxial wafer according to theabove (9) or (10), wherein the epitaxial layer is formed at 1120 Celsiusor higher temperature.

(12) The method of manufacturing the epitaxial wafer according to theabove (11), wherein the epitaxial layer is formed as a raw materialconcentration is controlled to be equal to or less than a predeterminedconcentration.

(13) The method of manufacturing the epitaxial wafer by utilizing asilicon wafer substrate of (110) crystal orientation wherein a variationin an edge part of an epitaxial layer thickness distribution of angleperiodicity can be reduced.

(14) An epitaxial wafer manufactured by the method as recited in theabove (9), wherein the manufactured epitaxial wafer has higher flatnessthan the semiconductor serving as a substrate.

(15) An epitaxial wafer manufactured by the method as recited in theabove (9), wherein an epitaxial layer thickness distribution in acircumferential direction in a peripheral part of the manufacturedepitaxial wafer indicates enough flatness that the epitaxial wafer issuitable for a device process.

(16) An epitaxial wafer characterized in that a variation of anepitaxial layer thickness distribution in a circumferential direction ina peripheral part is equal to or less than 0.5%.

Here, the peripheral part may, for example, be designated to a portion 1mm inner from the outer edge of the epitaxial wafer. Other than this, ifthe diameter of the disk-like epitaxial wafer is d, a concentric circlewith the diameter of 98% of ‘d’ and vicinity thereof may be theperipheral part. And since the variation of the layer thicknessdistribution tends to be larger as the diameter of the peripheral partbecomes larger, if the peripheral part is designated to be theconcentric circle and vicinity thereof with the diameter thereof 99.5%of ‘d’, a wider area can have the flatness. Further, if the outside ofthe concentric circle with the diameter thereof 99.5% of ‘d’ isdesignated to the peripheral part, even larger area has the flatness.

(17) A method of determining a manufacturing condition for growing anepitaxial layer with reaction of a semiconductor wafer and a source gasin a reaction furnace to manufacture an epitaxial wafer, the methodcomprising the steps of: manufacturing an epitaxial wafer in apredetermined initial manufacturing condition; measuring flatness alonga circumferential direction in a peripheral part of the manufacturedepitaxial wafer in the initial condition; determining an effect on theflatness in the peripheral part of the manufactured epitaxial wafer withrespect to the orientation-dependent control means and/or theorientation-independent control means; and determining the manufacturingcondition to increase the flatness in the peripheral part of theepitaxial wafer by combining or selecting from the orientation-dependentcontrol means and the orientation-independent control means inaccordance with a result of measured flatness in the peripheral part ofthe manufactured epitaxial wafer in the predetermined initialmanufacturing condition.

(18) An apparatus for manufacturing an epitaxial wafer by growing anepitaxial layer with reaction of a semiconductor wafer and a source gasin a reaction furnace comprising: a susceptor having a pocket having anopening in which the semiconductor wafer is positioned, wherein thesemiconductor wafer is fixed to the susceptor and the susceptor has astructure and/or shape changing periodically according to the change ofthe crystal orientation of the semiconductor wafer near an inner face ofthe opening.

The formation rate of the epitaxial layer may be different depending onthe crystal orientation. For example, in the silicon single crystal, asrepresented by a facet {111} and a facet {311} on (100) crystal face, itis know that the formation rate in the peripheral part of the wafershows the dependency of the crystal orientation according to the shapeof the chamfered portion.

High or low layer thickness with a cycle of 90 degree occurs in theperipheral part of the epitaxial wafer obtained as a result of theproduction. In order to prevent this effectively, it is preferable toprovide a compensation means in accordance with the crystal orientationnear the peripheral part of the semiconductor wafer serving as asubstrate.

On the other hand, the semiconductor wafer serving as the substrate isrotated at a predetermined rotational speed in order to obtain theuniform layer thickness in general as the epitaxial layer is formed inthe chamber of the epitaxial manufacturing apparatus. Therefore, thecrystal orientation always changes relative to the epitaxialmanufacturing apparatus. And, if the compensation means is fixed on theepitaxial manufacturing apparatus itself, it is a moveable member insynchronization with the semiconductor wafer rotation. On the otherhand, since the semiconductor wafer is fixed to the susceptor having thepocket as described below, the crystal orientation of the semiconductorwafer is fixed to the susceptor. Since the semiconductor wafer isrotated together, it is beneficial if the structure and/or shape andother features are changed according to the crystal orientation, i.e.,the susceptor so as to adjust the formation rate. Here, the structure isan integrated body being combined with various elements related witheach other and a mutual relationship with each element. For example, thestructure includes a combination of materials, members, and so on. Also,the shape is a configuration or figure of things and a state ofexistence. For example, it includes a triangle, a circle, a box shape,and so on. Big or small dimension may be included as different shapes.Here, the pocket provided in the susceptor basically has a flat bottomface and is in a circular recess (shape capable of accommodating adisk-like wafer). That is, the circular recess of the pocket may becomprised basically of an approximately vertical face (hereinafterreferred to as “inner face”) and a bottom face.

In general, since the formation rate of the epitaxial layer is dependenton the flow rate of the gas for growth, concentration of siliconconstituent, temperature, and so on, it is preferable to provide memberscapable of changing these near the inner face of the opening of thepocket of the susceptor where the semiconductor wafer is placed. Morespecifically, details are described below.

(19) The apparatus for manufacturing the epitaxial wafer according tothe above (18), wherein the susceptor has a spot facing with a depththereof changing near the inner face of the opening in synchronizationwith the change of the crystal orientation of the semiconductor wafer.

Here, the depth of the spot facing may be a distance from the top faceof the member defining the pocket of the susceptor to the ledge holdingthe semiconductor wafer. The thickness of the semiconductor wafer isuniform in the circumferential direction and the height of the ledgewhich supports the wafer is uniform. Therefore, in order to change thedepth of the spot facing, the position of the top face of the memberdefining the pocket is changed. That is, the top face of the member ofthe susceptor which defines the pocket repeats up and down along thecircumferential direction with a predetermined periodic cycle. Thepredetermined periodic cycle is synchronized with the periodic cycle ofthe crystal orientation which may affect the formation rate of theepitaxial layer and more specifically, it may include approximately 90degrees, approximately 180 degrees, and approximately 270 degrees.Likewise in “predetermined cycle” to be described below.

The up and down may be a curve such as a sine curve and a linear typesuch as box element or triangle element. For example, in the siliconsemiconductor wafer, it is preferable that the depth of spot facing isshallow in the [100] direction and the depth of spot facing is deep inthe [110] direction.

(20) The apparatus for manufacturing the epitaxial wafer according tothe above (18), wherein the susceptor is characterized in that a pocketwidth changes near the inner face of the opening in synchronization withthe change of the crystal orientation of the semiconductor wafer.

Here, the pocket width of the susceptor may be a pocket width viewed inthe top view of the pocket of the susceptor in which the semiconductorwafer is placed. At this time, since the semiconductor wafer showsapproximately a circle in the top view, if the pocket width changes witha cycle of approximately 90 degrees, the distance between the outercircumferential face and the inner face of the opening of the pocketchanges wide and narrow with a cycle of approximately 90 degrees.

This change of wide-and-narrow could be a curve or curve-like if it isdeveloped in the direction of circumferential direction, and could belinear comprised of a box element or a triangular element. For example,in the case of the silicon semiconductor wafer, it is preferable thatthe distance in the [100] direction becomes wider and that in the [110]direction is narrower.

Further, the semiconductor does not show an approximately circular inthe top view, it is preferable that the gap between the outer face ofthe semiconductor wafer and the inner face of the opening of the pocketchanges with a cycle of 90 degrees rather than the pocket width changeswith a cycle of 90 degrees. The way of changing is similar to whatmentioned above.

(21) The apparatus for manufacturing the epitaxial wafer according tothe above (18), wherein the susceptor has heat capacity changing nearthe inner face of the opening in synchronization with the change of thecrystal orientation of the semiconductor wafer.

Here, the heat capacity change may be a partial heat capacity changewith a cycle of 90 degree in the circumferential direction of theopening of the pocket. For example, it may include that the diameter ofthe susceptor is changed near the opening with a cycle of 90 degree.Although the shape of the susceptor does not change in thecircumferential direction, it may include changing the heat capacity bychanging the kinds of materials. For example, it is possible to berry alump of iron in the susceptor made of carbon.

This heat capacity change, if developed in the circumferentialdirection, may be a curve such as a sine curve and a linear line such asstraight line comprised of a box element or a triangular element. Forexample, in the silicon semiconductor wafer, it is preferable that theheat capacity is big in the direction and the heat capacity is small inthe [110] direction.

As mentioned above, although the depth of spot facing, the pocket width,and the heat capacity are treated as separate conditions, theseconditions can be combined with any other one or two. For example, thedepth of the spot facing and the pocket width; the pocket width and theheat capacity; the heat capacity and the depth of the spot facing; andthe depth of spot facing and the heat capacity can be made.

(22) A susceptor to be utilized in the epitaxial wafer manufacturingapparatus in which the epitaxial grows with reaction of thesemiconductor wafer and the source gas in the reaction furnace, thesusceptor comprising: a pocket having an opening in which thesemiconductor wafer is placed; a member having a shape changing near theinner face of the opening with a cycle of a predetermined period alongthe circumferential direction.

(23) A method of manufacturing an epitaxial wafer by growing anepitaxial layer with reaction of a semiconductor wafer and a source gasin a reaction furnace to manufacture an epitaxial wafer, the methodcomprising the steps of: providing the semiconductor wafer from anopening of a pocket; changing a structure and/or shape near the innerface of the opening along a circumference with a predetermine periodiccycle, wherein the change of the structure and/or shape is synchronizedwith the crystal orientation of the semiconductor wafer; fixing thesemiconductor wafer to the susceptor; and forming the epitaxial layer asthe susceptor is rotated with the semiconductor wafer.

As described above, an example of the epitaxial growth on the (100) faceof silicon is explained. However, the present invention is not limitedthereto, but it may apply to any kind of epitaxial manufacturingapparatus and the susceptor utilized therein and other equipment. Theapparatus can be applied to form the epitaxial layer of any kind ofmaterial having the epitaxial forming rate which had dependency on thecrystal orientation. Here, the epitaxial wafer having a peripheral partcharacterized by the uniform thickness without any dependency on thecrystal orientation may be manufactured by changing the cyclic period,degree of increase-and-decrease, and other conditions in accordance withthe features of the crystal orientation dependency.

(24) A method of manufacturing an epitaxial wafer by growing anepitaxial layer with reaction of a semiconductor wafer and a source gasin a reaction furnace to manufacture an epitaxial wafer, the methodcomprising the steps of: providing the semiconductor wafer on a ledgepart of a susceptor having an opening in which the semiconductor waferis positioned; providing the ledge part at a lower part of the openingsuch that the ledge part extends with a predetermined length inside ofthe opening of the susceptor and the semiconductor wafer is placedthereon; and controlling an epitaxial layer thickness grown by changingthe predetermined length of the ledge part.

Here, the semiconductor wafer is held by the ledge (‘Ledge’) part formedin the pocket having an opening of the susceptor. For example, thepocket may basically have a circular recess (capable of accommodatingthe disk-like wafer) having a flat bottom face. That is, the circularrecess of the pocket is defined by an approximately vertical face(hereinafter referred to as “inner face”) and a bottom face. The ledgepart may comprise a member provided on a bottom face along thecircumferential direction of the opening a top face of a tapered shape(a cup shape with a gently inclined side wall) extending inwardly as faras the predetermined length from the inner face. The ledge part drops toform a so-called shelf if it goes inwardly for the above predeterminedlength although the top face is tapered to securely support thesemiconductor wafer with the minimum contact area. That is, there it isdirected to the bottom face of the pocket by the approximately verticalwall. In this way, the ledge part has a shelf shape with a step formedby the drop. This is similar to the shelf shape formed by the fixedwasher to the bottom face just like the washer dropped in a circularrecess. Since the top face is tapered, the washer could be shaped like adisc spring. The ledge part may not be a separate part, but it may beintegrally formed in body with the susceptor. The semiconductor wafer issupported on the ledge part by contacting directly or indirectly withthe ledge part on a part of the back face (e.g., a toric ring). Thus,the ledge part is very close to the back face of the semiconductorwafer, but the bottom part of the opening dropping from the ledge partis much far from the back face of the semiconductor wafer.

When the ledge part is in a high temperature by the heat provided fromthe susceptor, the distance from the back face of the semiconductor isso short that the heat from the ledge part could be transferred withease and the circumferential part of the semiconductor wafer whichoverlaps with the ledge part (hereinafter referred to as “ledge area”)tends to be in the high temperature. Therefore, it is plausible that theledge area of the semiconductor wafer causes the forming rate of theepitaxial layer on the top face to increase since the heat transferredfrom the back face and the side face makes the ledge area hot.Therefore, the thickness of the epitaxial layer increases abruptly as itgoes outwardly. Here, the ledge area where the semiconductor waferoverlaps with the ledge part is on the top face of the semiconductorwafer (the opposite face to the back face of the semiconductor waferwhere the ledge part touches) and a circumferential part on the top faceof the semiconductor wafer at the position corresponding to a positionwhere the ledge is provided.

(25) The method of manufacturing the epitaxial wafer according to theabove (24), wherein at least one of both faces of the semiconductorwafer is constituted of a device useable area and the peripheral partsurrounding the device useable area; and wherein the predeterminedlength of the ledge part is adjusted not to reach a positioncorresponding to a position of the device useable area on the epitaxialwafer.

As mentioned above, the thickness of the epitaxial layer in the ledgearea of the semiconductor wafer tends to change drastically and theflatness on the manufactured epitaxial silicon wafer is more demanding.Therefore, it is not easy to maintain high flatness of the manufacturedepitaxial silicon wafer only by adjusting the thickness of thesemiconductor wafer serving as a substrate. It is also strongly demandedthat the flatness in the peripheral part of the epitaxial silicon waferis to be improved and that the cut-off part in the peripheral part is tobe reduced. Here, the flatness generally may mean a degree of beingflat. If the flatness is low, it is not flat, but if the flatness ishigh, it is understood that it is flat.

As mentioned above, if the ledge part does not extend to the deviceuseable area (or the ledge area is made small), the flatness in theuseable area of the epitaxial silicon wafer is increased.

(26) The method of manufacturing the epitaxial wafer according to theabove (24) or (25), wherein the predetermined length of the ledge partis variable along a circumferential direction on the opening such thatit can be modified in accordance with respective shapes of thesemiconductor wafer and the opening.

On the other hand, in the outer peripheral area of the semiconductorwafer, a big change in the shape (e.g., a big change in the thicknessdue to the chamfered edge) may cause a big change such as an abruptdecrease of the thickness of the epitaxial layer from ore near theposition. In such a case, it is possible to manufacture the epitaxialwafer with higher flatness as a result by cancelling out with the bigchange (abrupt increase) in the thickness of the epitaxial layeraccording to the change of the length of the ledge part as describedabove. Here, to be variable along the circumferential direction on theopening may mean, for example, that the distance from the inner face onthe top face of the ledge part varies clockwise along thecircumferential direction of the opening seen in the plan view.

(27) The apparatus for manufacturing the epitaxial wafer according toany one of the above (24) to (26), wherein the predetermined length ofthe ledge part is equal to or more than 2 mm and less than 6 mm.

For example, if the length of the ledge part is less than 6 mm, it ispossible to keep the position of the point of variation equal to or lessthan 6 mm from the outer periphery of the epitaxial silicon wafer sincethe big point of variation of the thickness tends to be formed at theborder of the ledge area. Therefore, it is rather easy to keep theflatness high in the useable area of the epitaxial silicon wafer insidethe border. Therefore, the point of change of the thickness can be movedout of the device useable area. Thus, it is possible to improve thethickness distribution of the epitaxial layer in the outer peripheralpart and prevent deterioration of the flatness by the epitaxial growth.If the length of the ledge part is short, for example, less than 4 mm,the high flatness can be maintained up to the peripheral area.

On the other hand, the ledge part has to keep the function to hold thesemiconductor wafer such that it is preferable that at least 2 mm of thelength is maintained. However, it is possible to make it even shorterthan this if the semiconductor wafer can keep the function to hold thesemiconductor wafer.

(28) An apparatus for manufacturing an epitaxial wafer by growing anepitaxial layer with reaction of a semiconductor wafer and a source gasin a reaction furnace comprising: a susceptor having an opening in whichthe semiconductor wafer is positioned; and a ledge part provided along acircumferential direction of the opening and extending inwardly for apredetermined length, the ledge part provided in a lower part of theopening such that the semiconductor wafer is placed, wherein at leastone of both faces of the semiconductor wafer is constituted of a deviceuseable area and the peripheral part surrounding the device useablearea, and the predetermined length of the ledge part is adjusted not toreach a position corresponding to a position of the device useable areaon the epitaxial wafer.

(29) The apparatus for manufacturing the epitaxial wafer according tothe above (28), wherein the predetermined length of the ledge part isequal to or more than 2 mm and less than 6 mm.

As mentioned above, according to the present invention, it is possibleto move the point of big change of the thickness of the epitaxial layeroutside of the device useable area and to contribute to theuniformization of thickness distribution in the device useable area suchthat the flatness of the epitaxial wafer may be improved. Also, it ispossible to increase (improve) the flatness of the epitaxial wafer bycombing with the shape of the semiconductor wafer serving as asubstrate. Thus, even though the thickness distribution of the epitaxiallayer is not so uniform (the degree of unevenness is high), or theflatness of the semiconductor wafer serving as a substrate is not sohigh, it is possible to yield much better flatness of the epitaxialwafer as a result by combining both.

Further, according to the present invention, it is possible to reducethe variation and make uniformization in the thickness in thecircumferential direction in the peripheral part of the epitaxial layer.Conversely, if the thickness change in the circumferential direction inthe peripheral part of the epitaxial layer is desired, it is possible toform a desirable thickness distribution in the periphery part of theepitaxial layer by utilizing the above apparatus and method.

In the above, the embodiments of the invention conceived by the presentinventor is explained. However, the present invention is not limited tosuch embodiments, and it should be understood that various alternationsand modifications could be made without departing the gist of thepresent invention.

What is claimed is:
 1. A method of manufacturing an epitaxial wafer bygrowing an epitaxial layer by reaction of a semiconductor wafer and asource gas in a reaction furnace comprising: providing the semiconductorwafer from an opening of a pocket of a susceptor of the reaction furnacein which the reaction takes place; fixing the semiconductor wafer to thesusceptor, the susceptor comprising a physical feature for affectinggrowth of the epitaxial layer on the semiconductor wafer in accordancewith a crystal orientation on the semiconductor wafer such that thephysical feature changes along a circumferential direction with apredetermined periodic cycle with which a periodic cycle of the crystalorientation of the semiconductor wafer along a circumferential directionthereof is synchronized; rotating the susceptor to which thesemiconductor wafer is fixed; and forming an epitaxial layer on thesemiconductor wafer with the source gas as the susceptor is rotated withthe semiconductor wafer such that the periodic cycles of the physicalfeature of the susceptor and the crystal orientation are synchronized soas to reduce difference in an epitaxial formation rate based on thecrystal orientation by the periodic cycle of the physical feature. 2.The method of manufacturing the epitaxial wafer according to claim 1,wherein the physical feature comprises a structure or shape changingperiodically near an inner face of the opening in accordance with thecrystal orientation on the semiconductor wafer.
 3. The method ofmanufacturing the epitaxial wafer according to claim 1, wherein theepitaxial layer is formed at 1120 Celsius or higher temperature.
 4. Themethod of manufacturing the epitaxial wafer according to claim 3,wherein the epitaxial layer is formed as a raw material gasconcentration is controlled to be equal to or less than a predeterminedconcentration.
 5. The method of manufacturing the epitaxial waferaccording to claim 1, wherein the epitaxial wafer is formed with asilicon wafer substrate of crystal orientation and a variation of alayer thickness of angle periodicity can be reduced.
 6. An epitaxialwafer manufactured by the method as recited in claim 1, wherein themanufactured epitaxial wafer has higher flatness than the semiconductorserving as a substrate.
 7. An epitaxial wafer manufactured by the methodas recited in claim 1, wherein an epitaxial layer thickness distributionin the circumferential direction in a peripheral part of themanufactured epitaxial wafer indicates enough flatness that theepitaxial wafer is suitable for a device process.
 8. An epitaxial wafermanufactured by the method as recited in claim 1, wherein a variation ofan epitaxial layer thickness distribution in a circumferential directionin a peripheral part is equal to or less than 0.5%.
 9. A method ofdetermining a manufacturing condition for growing an epitaxial layer byreaction of a semiconductor wafer and a source gas in a reaction furnaceto manufacture an epitaxial wafer, the method comprising: providing thesemiconductor wafer from an opening of a pocket of a susceptor of thereaction furnace in which the reaction takes place; fixing thesemiconductor wafer to the susceptor, the susceptor comprising aphysical feature for affecting growth of the epitaxial layer on thesemiconductor wafer in accordance with a crystal orientation on thesemiconductor wafer such that the physical feature changes along acircumferential direction with a predetermined periodic cycle with whicha periodic cycle of the crystal orientation of the semiconductor waferalong a circumferential direction thereof is synchronized; rotating thesusceptor to which the semiconductor wafer is fixed; manufacturing anepitaxial wafer in a predetermined initial manufacturing condition byforming an epitaxial layer on the semiconductor wafer with the sourcegas as the susceptor is rotated with the semiconductor wafer such thatthe periodic cycles of the physical feature of the susceptor and thecrystal orientation are synchronized so as to reduce difference in anepitaxial formation rate based on the crystal orientation by theperiodic cycle of the physical feature; measuring flatness along acircumferential direction in a peripheral part of the manufacturedepitaxial wafer in the initial condition; determining an effect on theflatness in the peripheral part of the manufactured epitaxial wafer withrespect to the physical feature; and determining the manufacturingcondition to increase the flatness in the peripheral part of theepitaxial wafer by adjusting the physical feature in accordance with aresult of measured flatness in the peripheral part of the manufacturedepitaxial wafer in the predetermined initial manufacturing condition.10. A method of manufacturing an epitaxial wafer by growing an epitaxiallayer with reaction of a semiconductor wafer and a source gas in areaction furnace to manufacture an epitaxial wafer, the methodcomprising: providing the semiconductor wafer on a ledge part of asusceptor having an opening in which the semiconductor wafer ispositioned; providing the ledge part at a lower part of the opening suchthat the ledge part extends with a predetermined length inside of theopening of the susceptor and the semiconductor wafer is placed thereon;and controlling an epitaxial layer thickness grown by changing thepredetermined length of the ledge part.
 11. The method of manufacturingthe epitaxial wafer according to claim 10: wherein at least one of bothfaces of the semiconductor wafer is constituted of a device useable areaand the peripheral part surrounding the device useable area; and whereinthe predetermined length of the ledge part is adjusted not to reach aposition corresponding to a position of the device useable area on theepitaxial wafer.
 12. The method of manufacturing the epitaxial waferaccording to claim 10, wherein the predetermined length of the ledgepart is variable along a circumferential direction on the opening suchthat it can be modified in accordance with respective shapes of thesemiconductor wafer and the opening.
 13. The method of manufacturing theepitaxial wafer according to claim 10, wherein the predetermined lengthof the ledge part is equal to or more than 2 mm and less than 6 mm. 14.The method of manufacturing the epitaxial wafer according to claim 10,wherein the predetermined length of the ledge part is equal to 3 mm. 15.The method of manufacturing the epitaxial wafer according to claim 1,wherein the physical feature of the susceptor comprises spot facingdepth, pocket width, or thermal capacity.
 16. The method ofmanufacturing the epitaxial wafer according to claim 15, wherein thephysical feature of the susceptor is the spot facing depth such that thedepth changes with a cycle of 90 degree in the circumferentialdirection.
 17. The method of manufacturing the epitaxial wafer accordingto claim 15, wherein the physical feature of the susceptor is the pocketwidth such that the width changes with a cycle of 90 degree in thecircumferential direction.
 18. The method of manufacturing the epitaxialwafer according to claim 15, wherein the physical feature of thesusceptor is the thermal capacity such that the thermal capacity changeswith a cycle of 90 degree in the circumferential direction.
 19. Themethod of manufacturing the epitaxial wafer according to claim 15,wherein the physical feature of the susceptor is the spot facing depthsuch that the depth changes with a cycle of 180 degree in thecircumferential direction.
 20. The method of manufacturing the epitaxialwafer according to claim 15, wherein the physical feature of thesusceptor is the pocket width such that the width changes with a cycleof 180 degree in the circumferential direction.
 21. The method ofmanufacturing the epitaxial wafer according to claim 15, wherein thephysical feature of the susceptor is the thermal capacity such that thethermal capacity changes with a cycle of 180 degree in thecircumferential direction.